We would like to thank Leslie Greengard and Marina Spivak for discussions on the fast Gauss transform. 
R.S. Sampath was supported by Oak Ridge National Laboratory's (ORNL) Postdoctoral Research Associates Program under contract numbers DE-AC05-00OR22725 and DE-AC05-00OR22750. Hari Sundar was supported by Siemens Corporate Research. S. K. Veerapaneni was supported by the National Science Foundation under the grants OCI-0749162 and CNS-0614770.
